22 November, 2023
This document explores the expert opinion gathered from staff at the Woodland Trust, related to the measurement of 14 indicators of woodland ecological condition, and the relationship between these indicators’ and a wood’s potential to promote flourishing wildlife species communities (by estimating “value functions” and importance weightings for each indicator).
Expert opinion on the value function and weight for each indicator
was elicitated using the Delphi method. The Delphi method is designed to
collect and distill expert knowledge, using repeated surveys to refine
estimates, increasing their reliability
and identifying where agreements and disagreements in understanding
occur.
The method relies on repetitive surveying in at least two to three ‘rounds’ where participants are asked the same questions. After each round participants review and consider the answers given by all panel-members, and are then given the opportunity to revise their answers. The Delphi method has a history of successful use in supporting conservation action where empirical evidence is insufficient and information is needed rapidly to inform decisions. It’s transparency and repeatability also add to its appeal.
Each participant either attended an introductory workshop to the process, or was taken through individually. A sub-section of participants were also involved in development the proposed methods to measure each indicator in the field. Answers were submitted into individual Excel spread sheets, with questions relating to:
Participants were encouraged to keep a clear distinction between the quantitative responses provided (i.e. value functions and weightings under typical conditions) and exceptions to those typical relationships (that they highlighted in their comments).
It was also stated that noted exceptions would be analysed and, where appropriate, used to inform future development of the WEC measure to account for important nuance.
Values and weights are all measured relative to each other. Some respondents did not use the full 0 to 100 range for all value functions and weights. Comparison between participants requires that they all use the same scale, and so all value functions where scaled from 0 to 100 and weightings were scaled so that the highest indicator weighting for each panelist was 100.
Value functions scaled for:
- Adam Th - Number deadwood classes present (of 3 potential classes)
across 4 plot-quarters,
- Adam Th - Number of native tree and shrub
species,
- Adam Th - Number of tree size classes (age proxy),
-
Adam Th - Vertical structure: Number of tree and shrub canopy layers
present,
- Alasdair Fi - Number deadwood classes present (of 3
potential classes) across 4 plot-quarters,
- Alasdair Fi - Number of
tree size classes (age proxy),
- Alasdair Fi - Tree regeneration,
- Alasdair Fi - Vertical structure: Number of tree and shrub canopy
layers present,
- Chris R - Number of ancient/veteran trees per 1 ha
plot,
- Chris R - Number of native tree and shrub species,
-
Chris R - Number of tree size classes (age proxy),
- Chris R -
Vertical structure: Number of tree and shrub canopy layers present,
- Dave Bo - Extent/ area of woodland,
- Dave Bo - Number
deadwood classes present (of 3 potential classes) across 4
plot-quarters,
- Dave Bo - Number of ‘positive indicator’ plants per
plot (10m radius circle),
- Dave Bo - Number of ancient/veteran
trees per 1 ha plot,
- Dave Bo - Number of native tree and shrub
species,
- Dave Bo - Number of tree size classes (age proxy),
-
Dave Bo - Tree regeneration,
- Dave Bo - Vertical structure: Number
of tree and shrub canopy layers present,
- Emma G - Number of native
tree and shrub species,
- Emma G - Number of tree size classes (age
proxy),
- Emma G - Occupancy of native trees & shrubs in all
canopy layers,
- Jim Sm-Wr - Extent/ area of woodland,
- Jim
Sm-Wr - Horizontal complexity (structural mosaics across a wood),
-
Jim Sm-Wr - Invasive plant species presence and cover,
- Jim Sm-Wr -
Number of ‘positive indicator’ plants per plot (10m radius circle),
- Jim Sm-Wr - Number of native tree and shrub species,
- Jim
Sm-Wr - Number of tree size classes (age proxy),
- Jim Sm-Wr -
Occupancy of native trees & shrubs in all canopy layers,
- Jim
Sm-Wr - Vertical structure: Number of tree and shrub canopy layers
present,
- Kylie Jo-Ma - Extent/ area of woodland,
- Kylie Jo-Ma
- Herbivore impact,
- Kylie Jo-Ma - Number of ‘positive indicator’
plants per plot (10m radius circle),
- Kylie Jo-Ma - Number of
ancient/veteran trees per 1 ha plot,
- Kylie Jo-Ma - Number of
native tree and shrub species,
- Kylie Jo-Ma - Number of tree size
classes (age proxy),
- Kylie Jo-Ma - Occupancy of native trees &
shrubs in all canopy layers,
- Kylie Jo-Ma - Tree regeneration,
- Kylie Jo-Ma - Vertical structure: Number of tree and shrub canopy
layers present,
- Liam Pl - Extent/ area of woodland,
- Liam Pl
- Herbivore impact,
- Liam Pl - Number of native tree and shrub
species,
- Liam Pl - Number of tree size classes (age proxy),
-
Liam Pl - Tree regeneration,
- Liam Pl - Vertical structure: Number
of tree and shrub canopy layers present,
- Lou Ha - Number of tree
size classes (age proxy),
- Lou Ha - Vertical structure: Number of
tree and shrub canopy layers present,
- Martin Hu - Horizontal
complexity (structural mosaics across a wood),
- Martin Hu - Number
deadwood classes present (of 3 potential classes) across 4
plot-quarters,
- Martin Hu - Number of native tree and shrub
species,
- Martin Hu - Occupancy of native trees & shrubs in all
canopy layers,
- Mick Br - Anthropogenic damage,
- Mick Br -
Herbivore impact,
- Mick Br - Horizontal complexity (structural
mosaics across a wood),
- Mick Br - Invasive plant species presence
and cover,
- Mick Br - Number deadwood classes present (of 3
potential classes) across 4 plot-quarters,
- Mick Br - Number of
‘positive indicator’ plants per plot (10m radius circle),
- Mick Br
- Number of ancient/veteran trees per 1 ha plot,
- Mick Br - Number
of native tree and shrub species,
- Mick Br - Number of tree size
classes (age proxy),
- Mick Br - Occupancy of native trees &
shrubs in all canopy layers,
- Mick Br - Tree disease and rapid
mortality,
- Mick Br - Tree regeneration,
- Peter Lo - Extent/
area of woodland,
- Peter Lo - Herbivore impact,
- Peter Lo -
Horizontal complexity (structural mosaics across a wood),
- Peter Lo
- Number of ‘positive indicator’ plants per plot (10m radius circle),
- Peter Lo - Number of ancient/veteran trees per 1 ha plot,
-
Peter Lo - Number of tree size classes (age proxy),
- Peter Lo -
Vertical structure: Number of tree and shrub canopy layers present,
- Rich Br - Number of tree size classes (age proxy),
- Rich Br -
Vertical structure: Number of tree and shrub canopy layers present,
- Saul H - Extent/ area of woodland,
- Saul H - Horizontal
complexity (structural mosaics across a wood),
- Saul H - Number of
tree size classes (age proxy),
- Saul H - Vertical structure: Number
of tree and shrub canopy layers present,
- Vanessa B - Herbivore
impact,
- Vanessa B - Number of tree size classes (age proxy),
-
Vanessa B - Vertical structure: Number of tree and shrub canopy layers
present
Weights were scaled for:
- Chris R,
- Dave Bo,
- Hannah Pa,
- Iain Mo,
-
Jim Sm-Wr,
- Liam Pl,
- Saul H
In some cases - where appropriate to allow categorisation - points were added to value functions by visual interpolation. Some points where also added by extrapolation where a maximum/minimum value was clearly implied.
A copy of this report was circulated to respondents between rounds to allow respondents to investigate estimates provided by others, and their certainties.
Where appropriate value functions where plotted categorically (with box plots summarising the estimated value at each category), and continuously (with lines connecting points and an indication of the general trend - see model details below). Indicator relative weightings were presented on boxplots, including the mean and median estimates. Interactive hover-text displayed respondent name and their certainty in their estimate.
Value functions were modeled with a binomial GAM. The influence of points from each respondent weighted by the inverse of the number of points provided by that respondent, with the aim of ensuring that all respondents had the same influence on the result, regardless of how many points they provided.
25 expert practitioners from Woodland Trust and Plantlife staff were
invited to provide their opinion the value and weight of
indicators.
20 have provided a response as of Wed Nov 22 16:31:25 2023.
Of these, 12 remain partially incomplete.
The chart below summarises participant completion of different elements of the survey. For more detail see table (button below chart).
Figure 1. Completion of expert opinion survey components by each
panelist (coloured portion of pies) for value functions (“Value func”),
value function certainties (“VF cert”), indicator weightings (“Weights”)
and weighting certainties (“wt certs”).
[1] “Number of tree size classes (age proxy)” [1] “17 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 1 | 0.0 | 0.0 |
| 2 | 40.0 | 15.5 |
| 3 | 76.5 | 15.0 |
| 4 | 100.0 | 0.0 |
[1] “Occupancy of native trees & shrubs in all canopy layers” [1] “17 respondants.”
VF:
- Similar trends. Some prefer linear, some S-shaped, some exponential,
some logarithmic - Bit of disagreement RE requirement for max value
Weightings: fairly wide spread
Of four possible categories: >15m; 5-15m; 2-5m; 0.5-2m; measured at plot level
[1] “Vertical structure: Number of tree and shrub canopy layers present” [1] “15 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 0.0 | NA |
| 1 | 1.7 | 6.5 |
| 2 | 43.9 | 21.9 |
| 3 | 86.9 | 10.3 |
| 4 | 100.0 | 0.0 |
| 5 | 100.0 | NA |
[1] “Number of native tree and shrub species” [1] “17 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 0.0 | 0.0 |
| 1 | 1.5 | 4.1 |
| 2 | 11.2 | 9.6 |
| 3 | 35.6 | 16.0 |
| 4 | 49.0 | 22.9 |
| 5 | 80.2 | 16.3 |
| 6 | 80.7 | 24.5 |
| 7 | 93.8 | 7.3 |
| 8 | 87.4 | 18.1 |
| 9 | 97.3 | 4.6 |
| 10 | 93.8 | 8.9 |
| 11 | 98.0 | 2.8 |
| 12 | 98.6 | 3.4 |
| 13 | 99.0 | 1.4 |
| 14 | 99.9 | 0.3 |
| 15 | 100.0 | 0.0 |
[1] “Invasive plant species presence and cover” [1] “17 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 100.0 | 0.0 |
| 1 | 55.0 | 7.1 |
| 5 | 58.2 | 36.3 |
| 10 | 66.5 | 30.1 |
| 15 | 90.0 | NA |
| 20 | 39.4 | 22.9 |
| 25 | 34.3 | 33.9 |
| 30 | 29.1 | 25.7 |
| 35 | 45.0 | NA |
| 40 | 16.4 | 16.9 |
| 45 | 10.0 | 14.1 |
| 50 | 16.1 | 23.0 |
| 55 | 12.0 | NA |
| 60 | 7.5 | 11.8 |
| 65 | 8.0 | NA |
| 70 | 9.2 | 14.2 |
| 75 | 5.0 | NA |
| 80 | 4.9 | 7.1 |
| 85 | 3.0 | NA |
| 90 | 3.0 | 3.9 |
| 95 | 1.0 | NA |
| 100 | 0.0 | 0.0 |
[1] “Number deadwood classes present (of 3 potential classes) across 4 plot-quarters” [1] “15 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 0.0 | 0.0 |
| 1 | 11.1 | 10.8 |
| 2 | 19.0 | 12.7 |
| 3 | 43.5 | 20.5 |
| 4 | 41.5 | 22.0 |
| 5 | 68.0 | 31.5 |
| 6 | 67.9 | 25.1 |
| 7 | 72.7 | 23.7 |
| 8 | 79.7 | 26.1 |
| 9 | 85.0 | 11.8 |
| 10 | 91.3 | 15.7 |
| 11 | 97.3 | 4.6 |
| 12 | 97.3 | 10.3 |
[1] “Number of ancient/veteran trees per 1 ha plot” [1] “15 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0.0 | 0.0 | 0.0 |
| 0.5 | 26.0 | NA |
| 1.0 | 38.4 | 20.4 |
| 1.5 | 66.0 | NA |
| 2.0 | 47.3 | 23.9 |
| 2.5 | 86.0 | NA |
| 3.0 | 77.5 | 17.2 |
| 3.5 | 100.0 | NA |
| 4.0 | 83.2 | 25.5 |
| 5.0 | 84.0 | NA |
| 6.0 | 80.1 | 17.8 |
| 7.0 | 91.0 | NA |
| 8.0 | 92.4 | 10.0 |
| 9.0 | 96.0 | NA |
| 10.0 | 97.3 | 4.5 |
| 11.0 | 99.0 | NA |
| 12.0 | 98.0 | 6.3 |
[1] “Extent/ area of woodland” [1] “13 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 0.0 | 0.0 |
| 1 | 3.8 | 4.8 |
| 2 | 5.5 | 7.8 |
| 3 | 24.0 | NA |
| 5 | 21.9 | 17.2 |
| 8 | 74.0 | NA |
| 10 | 40.3 | 23.7 |
| 15 | 64.5 | 12.0 |
| 20 | 70.6 | 25.2 |
| 25 | 70.7 | 18.1 |
| 30 | 82.1 | 22.5 |
| 35 | 91.0 | NA |
| 40 | 89.7 | 15.0 |
| 45 | 97.0 | NA |
| 50 | 100.0 | 0.0 |
[1] “Tree regeneration” [1] “15 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 0.0 | 0.0 |
| 1 | 38.9 | 33.2 |
| 2 | 71.0 | 24.5 |
| 3 | 100.0 | 0.0 |
[1] “Herbivore impact” [1] “14 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 55.2 | 44.5 |
| 1 | 83.2 | 30.9 |
| 2 | 55.2 | 27.6 |
| 3 | 36.5 | 33.0 |
| 4 | 22.2 | 42.2 |
[1] “Tree disease and rapid mortality” [1] “14 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 82.2 | 34.5 |
| 1 | 0.0 | NA |
| 5 | 65.0 | 49.5 |
| 10 | 76.0 | 29.5 |
| 15 | 30.0 | 14.1 |
| 20 | 47.0 | 30.8 |
| 25 | 61.7 | 38.2 |
| 30 | 36.2 | 39.0 |
| 40 | 33.9 | 33.9 |
| 50 | 32.5 | 23.6 |
| 60 | 26.0 | 31.5 |
| 70 | 22.5 | 10.6 |
| 75 | 25.0 | NA |
| 80 | 20.1 | 36.0 |
| 90 | 7.5 | 3.5 |
| 100 | 7.1 | 26.7 |
[1] “Number of ‘positive indicator’ plants per plot (10m radius circle)” [1] “14 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 0.0 | 0.0 |
| 1 | 13.3 | 10.4 |
| 2 | 21.2 | 20.2 |
| 3 | 35.8 | 43.0 |
| 4 | 41.7 | 7.6 |
| 5 | 41.7 | 12.2 |
| 6 | 70.0 | 14.1 |
| 7 | 66.5 | 30.4 |
| 8 | 90.0 | 10.0 |
| 9 | 92.0 | NA |
| 10 | 85.0 | 11.8 |
| 11 | 94.0 | NA |
| 12 | 87.5 | 10.6 |
| 13 | 96.0 | NA |
| 14 | 97.0 | NA |
| 15 | 95.1 | 5.5 |
| 16 | 99.0 | NA |
| 17 | 97.5 | 3.5 |
| 18 | 100.0 | NA |
| 19 | 100.0 | NA |
| 20 | 100.0 | 0.0 |
[1] “Horizontal complexity (structural mosaics across a wood)” [1] “13 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 0.0 | 0.0 |
| 1 | 5.5 | 9.6 |
| 2 | 32.9 | 13.1 |
| 3 | 70.1 | 21.0 |
| 4 | 89.4 | 12.7 |
| 5 | 100.0 | 0.0 |
[1] “Anthropogenic damage” [1] “16 respondants.”
| measure | Mean | Standard deviation |
|---|---|---|
| 0 | 93.8 | 25.0 |
| 2 | 50.0 | NA |
| 5 | 70.0 | 34.6 |
| 10 | 71.5 | 33.4 |
| 15 | 27.5 | 38.9 |
| 20 | 35.6 | 27.9 |
| 25 | 51.7 | 28.4 |
| 30 | 28.3 | 36.9 |
| 35 | 10.0 | NA |
| 40 | 27.9 | 22.0 |
| 45 | 4.0 | NA |
| 50 | 24.7 | 21.8 |
| 55 | 2.0 | NA |
| 60 | 16.6 | 22.7 |
| 61 | 0.0 | NA |
| 65 | 0.0 | NA |
| 70 | 21.7 | 25.7 |
| 75 | 11.7 | 12.6 |
| 80 | 15.0 | 31.9 |
| 85 | 0.0 | NA |
| 90 | 1.0 | 1.4 |
| 95 | 0.0 | NA |
| 100 | 6.7 | 25.8 |
Comments
Consensus on VF likely:
- All continuous relationships have same shape.
- Complete agreement on upper and lower value.
- Some put maximum value at 3 classes.
Disagreement on weight:
- Two camps, giving relatively low and high weights (compared to other indicators) at c. 60 and 90, respectively.